In general, the present invention relates to sensors for household appliances using cleaning media and, in particular, to sensors for sensing of the turbidity and temperature of cleaning media, e.g. used in washing machines and dishwashers.
An essential feature of efficiency of a washing machine or a dishwasher is a low consumption of energy and water which essentially depends on the dirt level of products to be cleaned. Since the dirt level of a product to be cleaned can hardly be directly determined or can not be determined directly at all, it is known to employ so-called turbidity sensors to determine the dirt level of a product to be cleaned indirectly by means of the turbidity or dirtying of a cleaning medium.
By means of turbidity sensors, in general, utilizing a sensing beam propagating through a cleaning medium, the turbidity and dirtying, respectively, of the cleaning medium, for example cleaning or washing water, is determined. On the basis of the determined turbidity or dirtying of the cleaning medium, the current dirt level of the product to be cleaned is determined and the operation of a washing machine or a dishwasher is accordingly controlled to obtain an effective cleaning with a minimized consumption of energy and water.
Further, the effectiveness of the cleaning by means of a washing machine or a dishwasher depends from the temperature of the cleaning medium, since the temperature of the cleaning medium and, in particular, a temperature corresponding to a given temperature or a given temperature course corresponding to a given temperature course determines the removal of dirt particles from the product to be cleaned.
For that purpose, temperature sensors are employed which are arranged in the washing or cleaning area of a respective machine and sense the temperature of the cleaning medium. Further, temperature sensors shell ensure that the temperature of the cleaning medium does not exceed a value given for the product to be cleaned, in order, for example, not to damage pieces of clothes by too high temperatures during the washing.
Usually, washing machines or dishwashers are equipped with turbidity sensors and temperature sensors embodied as separate components which accomplish the respective measurements of the cleaning medium at different locations in the household appliance. This can lead to a non-effective operation, in particular in the case the turbidity values determined by a turbidity sensor and the temperature determined by a temperature sensor are combined to optimize the operation of the machine.
In addition, known sensors which determine the turbidity and the temperature of a cleaning medium of a washing machine or a dishwasher exhibit large sizes which occupy a respective area in the machine. Moreover, such sensors having large dimensions can distort the results of the measurements in the case, in the areas in the machine wherein the sensors are located, static and dynamic conditions of the cleaning medium result due to the sensor dimensions, which are different compared to the areas wherein the actual cleaning is performed.
A further problem of such combined sensors is that the components for a temperature registration are often distorted by the temperature generation from the sensors itself and/or temperature changes of cleaning medium are determined too slow because of its arrangement in the sensor.
Object of the present invention is to overcome the above mentioned drawbacks of known solutions. In particular, the present invention shall provide a sensor for household appliances, such as washing machines or dishwashers, which determines fast and reliable both the turbidity and the temperature of a cleaning medium, has small dimensions and can be installed in a simple manner in a household appliance.
The object of the present invention is solved by a sensor which comprises a housing having two housing fingers extending from a basis. The both housing fingers, namely a first housing finger and a second housing finger are formed such that they are extending into a cleaning medium for the case of a sensor installed in a washing machine or a dishwasher.
In the first housing finger, a first optical element is arranged, while in the second housing finger, a second optical element is arranged.
For a measurement of the turbidity or dirtying of the cleaning medium, a sensing beam is employed which propagates between the optical elements from one housing finger to the other through the cleaning medium. Interactions of the sensing beam on its propagation path through the cleaning medium are employed to deduce the turbidity or dirtying of the cleaning medium.
Further, in the second housing finger, a temperature sensor for sensing the temperature of the cleaning medium is arranged such that the distance between the temperature sensor and the basis is larger than the distance between the second optical element and the basis.
In this manner, it is accomplished that the portion of the second housing finger wherein the temperature sensor is arranged is extending further into the cleaning medium compared to the portion of the second housing finger comprising the second optical element. This makes it possible to sense the temperature of the cleaning medium faster and more reliable since, for example, a heating of portions surrounding the temperature sensor or the temperature sensor itself by heat generating portions of the sensor is largely avoided.
The housing fingers can be designed such that the longitude axis thereof include an angle, wherein the distance between the free ends of the housing fingers can be larger or smaller than between the portions of the housing fingers which are connected to basis. In the case, the housing fingers are extending in a V-shape from the basis, a larger measuring path is obtained, even for an opposing arrangement of the first and second optical elements which enables for a more precise registration of the turbidity or dirtying of the cleaning medium.
To obtain a larger measuring path, it is further contemplated to arrange the first and second optical elements in a displaced manner in relation to the longitudinal axis of the housing fingers such that the measuring path between the optical elements is extending diagonally between the housing fingers. This extension of the measuring path is in particular suitable in the case where the first and second housing fingers are extending essentially parallel from the basis, which is why, in contrast to, for example, two housing fingers being arranged in a V-form, an essentially constant distance between the housing fingers is given.
Further, it is contemplated to arrange the first and second optical elements relatively to each other such that they lie on an axis which coincides with a straight propagation path for the sensing beam. Alternatively, is it possible to arrange the first and second optical elements relatively to such an axis in a displaced manner in order to register special interactions of the sensing beam on its propagation path through the cleaning medium (for example scattering effects).
To enable for more compact design of the sensor it, is contemplated that the first and second housing fingers have a different lengths wherein the second housing finger comprising the temperature sensor is longer than the other, first housing finger.
A reduced design can particularly be obtained in the case where the first optical element is arranged in an end portion of the first housing finger, i.e. in a portion of the first housing finger which is most remote from the basis.
Preferably, in the case of an utilization of housing fingers been different long, the temperature sensor is arranged as remote as possible from the basis, i.e. in an end portion of the second housing finger, wherein the second optical element is located between the temperature sensor and the basis.
The different length of the housing fingers promotes a balance of cleaning medium being located between the housing fingers during the cleaning procedure such that the turbidity or dirtying of the cleaning medium determined by means of the optical elements represents the actual turbidity or dirtying. This can be supported by a respective design of the basis and a suitable mounting position of the sensor in a household appliance, respectively.
A further advantage of housing fingers being different long is that the temperature sensor can be arranged further into the cleaning medium without essentially enlarging the design of the sensor.
Preferably, the temperature sensor is surrounded by a heat conduction paste or a gel, which can fill out the end portion of the second housing finger comprising the temperature sensor. The heat conduction paste provides for an improved heat transfer from the cleaning medium external to the housing via the housing, more precisely the material of the second housing finger, to the temperature sensor. Further, in this manner, the temperature sensor is not rigidly/firmly cast in the housing whereby problems due to different temperature co-efficients of the housing and the materials surrounding the temperature sensor are avoided. Furthermore, the material surrounding the temperature sensor is not brittle and provides for a better adhesion to the housing compared to rigid cast substances.
The utilization of a heat conduction paste for improving the temperature transfer to the temperature sensor allows a more simple design of the sensor since the heat conduction paste is only required to be injected or filled into the end portion of the second housing finger. This can take place prior or after arranging the temperature sensor.
Further, a separation means can be employed which separates the end portion of the second housing finger from the remaining portions of the sensor being enclosed by the housing. Preferably, the separation means provides for a seal, at least sealing with respect to the heat conduction paste, for the end portion of the second housing finger.
In dependence from the application of the sensor, for example in dependence from its orientation in a washing machine or a dishwasher, the separation means can be designed such that it prevents a flowing of the heat conduction paste out of the second housing finer. Alternatively or in addition, the separation means can also provide for a thermal insolation or separation of the portion of the second housing finger comprising the temperature sensor from the portion comprising the second optical element.
For arranging the optical elements and the temperature sensor in the housing, it is contemplated to employ a support being connected to these components, which is, for an assembly of the sensor, introduced into the housing and mounted therein, for example by means of clamp, snap and/or adhesive connections. Also, the support can provide for a positioning and orientation, respectively, of the optical elements and/or the temperature sensor in the housing.
In an advantageous manner, the separation means is provided by the support, for example by means of a flat structure being formed on the support which seals, comparable to a lid, the end portion of the second, longer housing finger.
Further, it is contemplated to connect the optical elements and the temperature sensor with a circuit board such that the electrical components of the sensor according to the invention can be arranged therein in a pre-manufactured manner.
The support for the optical elements and the temperature sensor can be connected with the circuit board or can be integrally incorporated. Further, it is possible that the function of the support is provided by the circuit board itself. The latter case also applies for the separation means which can be provided, for example, by means of a surface which essentially extends perpendicular to the actual circuit board.
Preferably, the circuit board comprises a plug connector extending from the housing in order to operatively connect the sensor with a washing machine or a dishwasher in a simple manner.
By means of a lid, the space enclosed by the housing can be sealed in order to, for example, prevent a penetration of undesired substances (i.e. drifting cleaning medium and dirt). Furthermore, the lid can be formed such that the plug connector of the circuit board is extending through the lid to the outside.
Moreover, the lid can have a shape which surrounds, comparable to a plug housing, the part of the plug connector which extends to the outside. In this manner, the lid can serve as a form fit connection to a washing machine or a dishwasher, wherein structures contemplated for the respective portions of the lid can provide for a coding for connecting the sensor with a washing machine or a dishwasher and/or for a snap or click connection.